1. Field of the Invention
The present invention related to a conductive resin composition and a chip-type electronic component, and more particularly, relates to a conductive resin composition suitable for use in the formation of a resin electrode to serve as an external electrode of a chip-type electronic component, and a chip-type electronic component including a resin electrode (an external electrode) formed from the same.
2. Description of the Related Art
In recent years, resin electrodes formed by applying and curing a resin composition containing a conductive component have been used as external electrodes in chip-type electronic components such as chip-type laminated ceramic capacitors.
As one of such chip-type electronic components, a chip-type capacitor has been proposed which has a structure as shown in FIG. 2 (see Japanese Patent Application Laid-Open (JP-A) No. 2007-67239).
This chip-type capacitor includes a laminated ceramic device (chip substrate) 51 including ceramic layers 52 and internal electrodes 53a and 53b, end surface electrodes (fired electrodes) 55a and 55b formed by applying a conductive paste to both end surfaces 54a and 54b of the laminated ceramic device 51 and firing the conductive paste, and resin electrodes 56a and 56b provided so as to cover the end surface electrodes 55a and 55b. 
It is to be noted that the end surface electrodes 55a and 55b and the resin electrodes 56a and 56b constitute external electrodes electrically connected to the internal electrodes 53a and 53b in this chip-type capacitor.
In addition, when the outermost ceramic layer 52a of the laminated ceramic device (chip substrate) 51 in this chip-type capacitor has a thickness L, the end surface electrodes 55a and 55b are adapted to cover the surface of the outermost ceramic layer within L×tan θ (θ=30°), and the resin electrodes 56a and 56b are provided to cover the end surface electrodes 55a and 55b. 
Furthermore, the resin electrodes 56a and 56b in this chip-type capacitor covering the end surface electrodes 55a and 55b have flexibility, and thus the resin electrodes 56a and 56b have sufficient adhesion to the laminated ceramic device (chip substrate) 51 and the end surface electrodes 55a and 55b, not to be detached by stress. In addition, the resin electrodes 56a and 56b function to prevent the occurrence of cracks starting from the ends of the end surface electrodes 55a and 55b which are fired electrodes, and even if any cracks occur, the resin electrodes 56a and 56b are considered to be able to prevent the internal electrodes 53a and 53b from being broken by the cracks, because the areas for the end surface electrodes 55a and 55b provided are as described above.
As a conductive resin composition used for the formation of the resin electrodes 53a and 53b, a conductive resin composition containing a metal powder, an epoxy resin, a curing agent, and a solvent has been proposed which has a thixotropic index of 1.8 or less, where the index is the viscosity measured at the number of revolutions of 1 rpm in a rotating viscometer is divided by the viscosity measured at the number of revolutions of 5 rpm (see claim 1 of JP-A No. 2005-264095).
A conductive resin composition has been proposed in which the epoxy resin is a mixture containing an epoxy resin component (A) with an epoxy equivalent of 900 g/eq or more and an epoxy resin component (B) with an epoxy equivalent less than 900 g/eq, and the content of the epoxy resin component (A) in the epoxy resin is 30 wt % or more (see claim 2 of JP-A No. 2005-264095).
In the case of the conductive resin composition in JP-A No. 2005-264095, the thixotropic index set to 1.8 or less is considered to make the applied shape favorable.
In addition, the epoxy equivalents specified as described above are considered to provide a conductive resin composition in which the thixotropic index is 1.8 or less.